[PATCH v1] perf build: Don't compile demangle-cxx.cpp if not necessary

Ian Rogers
2023-04-17T19:26:05Z

demangle-cxx.cpp requires a C++ compiler, but feature checks may fail
because of the absence of this. Add a CONFIG_CXX_DEMANGLE so that the
source isn't built if not supported. Copy libbfd and cplus demangle
variants to a weak symbol-elf.c version so they aren't dependent on
C++. These variants are only built with the build option
BUILD_NONDISTRO=1.

Signed-off-by: Ian Rogers <irogers@google.com>
---
tools/perf/Makefile.config | 1 +
tools/perf/util/Build | 2 +-
tools/perf/util/symbol-elf.c | 27 +++++++++++++++++++++++++++
3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 71442c54c25f..5f0f24b56f50 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -923,6 +923,7 @@ ifndef NO_DEMANGLE
EXTLIBS += -lstdc++
CFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
CXXFLAGS += -DHAVE_CXA_DEMANGLE_SUPPORT
+ $(call detected,CONFIG_CXX_DEMANGLE)
endif
ifdef BUILD_NONDISTRO
ifeq ($(filter -liberty,$(EXTLIBS)),)
diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index bd18fe5f2719..f9df1df1eec0 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -214,7 +214,7 @@ perf-$(CONFIG_ZSTD) += zstd.o

perf-$(CONFIG_LIBCAP) += cap.o

-perf-y += demangle-cxx.o
+perf-$(CONFIG_CXX_DEMANGLE) += demangle-cxx.o
perf-y += demangle-ocaml.o
perf-y += demangle-java.o
perf-y += demangle-rust.o
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 35724f6a84fa..cd08bdb9824f 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -31,6 +31,13 @@
#include <bfd.h>
#endif

+#if defined(HAVE_LIBBFD_SUPPORT) || defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
+#ifndef DMGL_PARAMS
+#define DMGL_PARAMS (1 << 0) /* Include function args */
+#define DMGL_ANSI (1 << 1) /* Include const, volatile, etc */
+#endif
+#endif
+
#ifndef EM_AARCH64
#define EM_AARCH64 183 /* ARM 64 bit */
#endif
@@ -271,6 +278,26 @@ static bool want_demangle(bool is_kernel_sym)
return is_kernel_sym ? symbol_conf.demangle_kernel : symbol_conf.demangle;
}

+/*
+ * Demangle C++ function signature, typically replaced by demangle-cxx.cpp
+ * version.
+ */
+__weak char *cxx_demangle_sym(const char *str __maybe_unused, bool params __maybe_unused,
+ bool modifiers __maybe_unused)
+{
+#ifdef HAVE_LIBBFD_SUPPORT
+ int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
+
+ return bfd_demangle(NULL, str, flags);
+#elif defined(HAVE_CPLUS_DEMANGLE_SUPPORT)
+ int flags = (params ? DMGL_PARAMS : 0) | (modifiers ? DMGL_ANSI : 0);
+
+ return cplus_demangle(str, flags);
+#else
+ return NULL;
+#endif
+}
+
static char *demangle_sym(struct dso *dso, int kmodule, const char *elf_name)
{
char *demangled = NULL;
--
2.40.0.634.g4ca3ef3211-goog